Foot-and-mouth disease (FMD) is a highly contagious disease caused by FMD virus (FMDV) in cloven-hoofed animals. Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are representative receptors in the cytoplasm for the detection of viral RNA and trigger antiviral responses, leading to the production of type I interferon. Although MDA5 is a crucial receptor for sensing picornavirus RNA, the interplay between MDA5 and FMDV is relatively unknown compared to the interplay between RIG-I and FMDV. Here, we observed that the FMDV infection inhibits MDA5 protein expression. Of the non-structural proteins, the Lb and 3C proteinases (Lbpro and 3Cpro) were identified to be primarily responsible for this inhibition. However, the inhibition by 3Cpro was independent of proteasome, lysosome and caspase-dependent pathway and was by 3C protease activity. A direct interaction between 3Cpro and MDA5 protein was observed. In conclusion, this is the first report that 3Cpro inhibits MDA5 protein expression as a mechanism to evade the innate immune response during FMDV infection. These results elucidate the pathogenesis of FMDV and provide fundamental insights for the development of a novel vaccine or therapeutic agent.

The baby hamster kidney-21 (BHK-21) cell line is a continuous cell line used to propagate foot-and-mouth disease (FMD) virus for vaccine manufacturing. BHK-21 cells are anchorage-dependent, although suspension cultures would enable rapid growth in bioreactors, large-scale virus propagation, and cost-effective vaccine production with serum-free medium. Here, we report the successful adaptation of adherent BHK-21 cells to growth in suspension to a viable cell density of 7.65 × 106 cells/mL on day 3 in serum-free culture medium. The suspension-adapted BHK-21 cells showed lower adhesion to five types of extracellular matrix proteins than adherent BHK-21 cells, which contributed to the suspension culture. In addition, a chemically defined medium (selected by screening various prototype media) led to increased FMD virus production yields in the batch culture, even at a cell density of only 3.5 × 106 cells/mL. The suspension BHK-21 cell culture could be expanded to a 200 L bioreactor from a 20 mL flask, which resulted in a comparable FMD virus titer. This platform technology improved virus productivity, indicating its potential for enhancing FMD vaccine production.

In South Korea, pigs were vaccinated once between 8 and 12 weeks of age because of the injection-site granulomas. Therefore this study was performed to determine the optimal age for single vaccination of growing pigs with the currently used type O FMD vaccine. With 498 pigs divided into four groups, seroprevalence of the antibody was analyzed with enzyme-linked immunosorbent assay. Although double vaccination is necessary to completely protect growing pigs from FMD virus infection with the current vaccine, the age of 8 weeks can be considered as the optimal age for piglet vaccination if the booster injection is unavailable.

To differentiate foot-and-mouth disease (FMD)-infected animals from vaccinated livestock, non-structural proteins (NSPs) must be removed during the FMD vaccine manufacturing process. Currently, NSPs cannot be selectively removed from FMD virus (FMDV) culture supernatant. Therefore, polyethylene glycol (PEG) is utilized to partially separate FMDV from NSPs. However, some NSPs remain in the FMD vaccine, which after repeated immunization, may elicit NSP antibodies in some livestock. To address this drawback, chloroform at a concentration of more than 2% (v/v) was found to remove NSP efficiently without damaging the FMDV particles. Contrary to the PEG-treated vaccine that showed positive NSP antibody responses after the third immunization in goats, the chloroform-treated vaccine did not induce NSP antibodies. In addition to this enhanced vaccine purity, this new method using chloroform could maximize antigen recovery and the vaccine production time could be shortened by two days due to omission of the PEG processing phase. To our knowledge, this is the first report to remove NSPs from FMDV culture supernatant by chemical addition. This novel method could revolutionize the conventional processes of FMD vaccine production.

A local virus isolate, O/SKR/JC/2014 (O JC), has been considered as a candidate vaccine strain in the development of a domestic foot-and-mouth disease (FMD) vaccine in Korea. However, producing and preserving a sufficient quantity of intact vaccine antigens from the O JC strain was difficult owing to its distinctive structural instability compared to other candidate vaccine strains. Based on this feature, the O JC strain was adopted as a model virus for the stabilization study to determine the optimal stabilizer composition, which enables long-term storage of the FMD vaccine antigen in both aqueous and frozen phases. In contrast to O JC vaccine antigens stored in routinely used Tris-buffered or phosphate-buffered saline, those stored in Tris-KCl buffer showed extended shelf-life at both 4 °C and −70 °C. Additionally, the combined application of 10% sucrose and 5% lactalbumin hydrolysate could protect O JC 146S particles from massive structural breakdown in an aqueous state for up to one year. The stabilizer composition was also effective for other FMDV strains, including serotypes A and Asia 1. With this stabilizer composition, FMD vaccine antigens could be flexibly preserved during the general production process, pending status under refrigeration and banking under ultrafreezing.